MAGNETORESISTANCE AND EXCHANGE EFFECTS OF NICO CU SANDWICH FILMS WITHOXIDE OVERLAYER/

Giant magnetoresistance (GMR) of 8% at 4.2 K is found in sandwich film s having the composition Ni0.7Co0.3(50 angstrom)/Cu(t)/NiCo(50 angstro m)/NiCoO(40 angstrom) where NiCoO is a mixed oxide overlayer that exch ange couples with the NiCo alloy layer. These films show a MR temperat ure dependence quite similar to that previously reported for Co/Cu/Co/ CoO where the MR becomes small above 200 K. When bilayers of CoO/NiO a re placed on the NiCo layer, the temperature dependence of MR extends to 250 K. The magnitude of the MR at 4.2 K scales with the magnitude o f the saturation magnetization in the NiCo and Co films.